Manual trim vs. elevator counterbalance

[LettersFromFlyoverCountry]

Wondering if anyone has had a problem of manual trim messing up two nicely counterbalanced elevators and, if so, what the solution is.

The particulars of my problem along with pictures are posted on the blog but basically, the attaching of the manual trim cable seems to want to pull the after part of the elevator lower.

I messed around yesterday with changing the amount of cable in the HS to no avail. I figured maybe it was acting like a "stick" to push the aft end down.

I have the "old style" counterbalance weights and I've already put the tips on and fiberglassed over them so there's some limitations I have adding weight. Plus there's the question of whether I should add weight to elevators that are already balanced?

 

[Bob Axsom]

I would not!

I have a manual trimmed elevator and consider balancing the elevators and the connection of the trim cable two unrelated functions. Note that I have an RV-6A but I assume the designs are similar. The manual trim system has such a sweet feel that it is almost a sensual pleasure to fine tune the pressure off the stick with it. If you have the elevators statically balanced, that job is done and should not be compromised by your thoughts about the trim system.

By the way, don't forget to fill that cavity behind the weight, it is a lot bigger source of drag than you would imagine.

Bob Axsom

 

[Walt]

By the way, don't forget to fill that cavity behind the weight, it is a lot bigger source of drag than you would imagine.

Bob Axsom

Just be sure that if you fill this area it is SECURE, the potential for a jammed elevator exists if it comes loose

 

[bill v]

good thread

I too worry about this. thanks for the reply Bob but why is it not a factor in the balance. you are adding weight to the system just by the cable being there. On my 4 I did nothing because no one else did and never have heard of a problem but have worried about this. Would appreciate more discussion on this topic. thanks

 

[Doug]

..and when you connect the elevator pushrod the mass of the pushrod also upsets the elevator balance, especially in a tail dragger as it sits on the ground.

I have disregarded the trim cable and push rod influence on the balance, be that right or wrong.

The manual trim system has such a sweet feel that it is almost a sensual pleasure to fine tune the pressure off the stick with it.

Isn't that the truth! Sometimes as I put the finest adjustment on the trim I wonder how well I could have done that if it had been electric.

 

[JonJay]

Move on Bob. There are a lot of dynamics associated with the trim cable as it isn't just dead weight. You already addressed what is, arguably, important, a balanced elevator.

 

[L.Adamson]

Isn't that the truth! Sometimes as I put the finest adjustment on the trim I wonder how well I could have done that if it had been electric.

For some reason, perhaps the installation , my electric trim worked amazingly well! On an RV6A even.

 

[Rupester]

Yep ... trim cable affects elev balance ...

.... I noticed it on mine when all was hooked up. It's clear the stiffness of the manual trim cable and the angle of its position applies a certain amount of force on the elevator. I decided there was nothing I could do to change/eliminate it, so I just moved on to other stuff. My elevator with cable connected sits "nicely in trail". That's all I'm really worried about.

 

[LettersFromFlyoverCountry]

My elevator with cable connected sits "nicely in trail". That's all I'm really worried about.

Wish mine did.

 

[alpinelakespilot2000]

Bob-
I've pmailed you the reply I got to this question from Ken at Van's. Basically, he said to balance first then attach trim cable but don't get too hung up on any of it. One of those things that builders apparently obsess over without good reason.
Hope it helps.
Steve